Development of technology related to utilization of solar energy, which is a clean, non-exhaustible resource, is indispensable for solving present and future energy problems. Among others, organic thin-film solar cells have advantages of lower material and manufacturing costs than other potential solar cells such as silicon-based solar cells, and are expected as promising candidates for solar cells.
However, organic thin-film solar cells have a problem that the power generation efficiency is low as compared with solar cells of other type already in practical use. Therefore, there are demands for improving power generation efficiency for practical application of organic thin-film solar cells. In addition, in order to widely put organic thin-film solar cells into practical use, it is necessary to further reduce material and manufacturing costs from the viewpoint of compensating for their low power generation efficiency.
Glass substrates are usually used as the base material of organic thin-film solar cells. However, glass substrates account for not a small part of the material cost of organic thin-film solar cells. Glass substrates also require special care for handling so as not to be broken during manufacture, transportation, or installation. Moreover, glass substrates are used while being held in a metal frame or a casing, and additional costs are incurred accordingly. Glass substrates also have transparent electrodes formed on their surface, and ITO (Indium Tin Oxide) is mainly used as the material of such transparent electrodes. ITO is not only expensive but also the price is unstable as it contains indium which is a rare metal. For these reasons, it is difficult to reduce the manufacturing cost of organic thin-film solar cells using glass substrates.
To address these issues, various techniques have been examined for using substrates made of less expensive materials instead of glass substrates. For example, a conventional technique proposes a substrate using a plastic material such as PET (PolyEthylene Terephthalate) as a base material. JP201135258A (PTL 1) describes a technique of using an aluminum substrate instead of a conventional ITO/glass substrate.